1. Field of the Invention
The present invention relates generally to a image sensor, more specially to a color filter array and its signal process circuit in which vertical interpolation process is not needed, which can be applied to the field of image signal input and signal process such as video camera, digital camera and color scanner, and color copier which process image signal.
2. Description of Prior Art
In general, each basic pixel of color image sensor is covered with color filter so that the complexities of the signal process depend on the pattern of the color filter structure. Though each pixel is divided as Red color filter pixel, green color filter pixel and blue color filter pixel in order to produce color image signals, each pixel has to have all of the color signals (R, G, B) in accordance with interpolation method to make signal process.
FIGS. 1a and 1b show the conventional structures of color filter array to make red, green and blue signal process (hereinafter red, green and blue signals are respectively referred as R, G and B signals). FIG. 1a shows a filter pattern consisting of R-G-B, G-B-R and B-R-G filter groups and FIG. 1b shows a filter pattern consisting of R-G and G-B filter groups.
In FIG. 1a, pixel values between each signal should be obtained because each R, G and B signal crosses every three pixels. For example, the interpolation equation to get color signal (C12, C21) for two pixels between first signal (C1) and second signal (C2) is as follows;
color signal (C12)=⅓(2C1+C2),
color signal (C21)=⅓(C1+2C2)
Since such an equation for interpolation process needs ⅓ multiplication calculation and it is difficult to process its valid number, circuit structure becomes complex.
Color filter arrays in FIG. 1 make a structure in which the human color sensibility level is considered and the number of pixel of G is double of the number of pixels of R and B respectively. However, there are some problems that the circuit becomes complex since both horizontal and vertical interpolation processes are needed in such a structure, and the circuit becomes large since the line delay buffers for vertical interpolation are used additionally.
An object of this invention is to provide a color filter array and its color interpolation apparatus which can operate at high speed and can interpolate the color signal without vertical interpolation as a simple structure.